With the ever expanding frontiers of space and aviation, and with modern aircraft now operating at altitudes which only a few decades ago were thought to be impossible, it is becoming increasingly important to overcome some problems introduced by high altitude flight. At high altitudes, the ambient light often is quite bright and may adversely affect the operation of optical avionics equipment.
One particular type of avionics equipment where the high ambient light is posing vexing problems, is in the use of thin film electroluminescent (TFEL) matrix display panels.
Electroluminescence is the emission of light from a luminescent material when an electric field of sufficient amplitude is applied to the material. This phenomenon has been used to construct display panels by using the luminescent material as the dielectric in a parallel plate capacitor in which one of the conducting plates is transparent. When alternating voltages or pulses are applied to the plates, the luminescent material emits light.
Electroluminescent video display panels have been constructed by depositing conductive rows and columns on opposite, non-conductive plates of a capacitor to form an x-y matrix. A typical TFEL matrix display panel of the prior art is shown in FIG. 1. The coordinates of the matrix are the pixels of the display. When a voltage differential is created between a row and a column, the luminescent material between the crossing electrodes emits light at that pixel.
Electroluminescent technology offers the potential of providing compact, flat panel displays rather than the bulky cathode ray tube now in wide use. Small electroluminescent display panels can be driven by integrated solid state circuits to provide miniature video systems that are not practical using cathode ray tube displays.
To realize the potential of electroluminescent displays, drive circuits are required which are inexpensive, reliable, require low power, and fully utilize the electroluminescent capacity of the display, including the output of a sufficiently bright display.
In the past, numerous techniques and drive circuits have been used to operate TFEL displays. One particular prior art technique is shown in FIG. 2, which consists of a voltage versus time plot of the voltages applied to the rows and columns of the panel. A threshold voltage, which varies depending on the phosphor used, is shown, and this threshold voltage is the voltage below which no new luminescence is initiated. In this technique, a voltage V.sub.B is applied to the row electrode B, and a voltage V.sup.c is applied to column electrode c individually, both of these voltages are less than the threshold voltage, but at the pixel P.sup.c.sub.B the combined voltages exceed the threshold and luminescence is thereby initiated at that point. Both V.sub.B and V.sup.c continue for a predetermined time period then they both are eliminated. Next a voltage V.sub.C is applied to row C and a voltage V.sup.d is applied to column d. This results in luminescence from pixel P.sup.d.sub.C.
With this technique only one row is addressed at any one time. The overall brightness of the display is limited by the refresh frequency which is in turn limited by the pulse width.
Consequently, there exists a need for improvement in TFEL drive circuits and techniques which provide for increased brightness and increased refresh frequency without altering the effective pulse width so much as to lose the benefit of the increased refresh frequency. cl OBJECTS OF THE INVENTION
It is an object of the present invention to provide a TFEL matrix display panel drive technique which allows for increasing the brightness of TFEL displays.
It is a feature of the present invention to include row or column voltage wave forms which exhibits a relatively short initial peak followed by a relatively long plateau region.
It is an advantage of the present invention to provide a sustaining voltage by the plateau region of the row or column voltage wave form, which allows for continued luminescence.
It is another object of the present invention to provide a technique which allows for the capability of addressing multiple rows at any one given time.
It is another feature of the present invention to have a relatively extended plateau region of the row or column voltage wave form, at a voltage level sufficiently below the threshold voltage level, so that, any row or column voltages which might be applied at the same time to any one given pixel does not, in combination, exceed the threshold voltage for the predetermined phosphor.
It is another advantage of the present invention to provide for the ability to address multiple rows at the same time, so long as only one row or column voltage has its wave form in the initial peak region.
It is yet another object of the present invention to provide for an increased refresh frequency rate.
It is another feature of the present invention to provide a voltage wave form applied to the row or columns so that the initial peak portion of the voltage wave form is relatively short in duration to the extended plateau region of the wave form.
It is yet another advantage of the present invention to allow for increased refresh frequency rate by addressing multiple rows at any one given time so long as the initial peak portion of the wave form of any one given row is the only initial peak wave form region of any voltage wave form on any row.